I use Seachem garlic guard periodically. It's supposed to help ward off disease (Hexamita caused). I also add VitaChem to the water and the food periodically.Yes a PB. Just regular household garlic? What does it do?
I'm not saying your fish have HLLE but white poop is not a good sign, thus the advice to monitor.
You can also buy fish foods infused with garlic.
Just remember - Water change, water change, water change. It's the most important. As well as having a clean tank and filter.